U.S. patent application number 10/956919 was filed with the patent office on 2006-03-30 for disk drive with support structure for disk-vibration capacitive sensors.
Invention is credited to Toshiki Hirano, Tetsuo Semba, Matthew T. White.
Application Number | 20060066991 10/956919 |
Document ID | / |
Family ID | 35539614 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060066991 |
Kind Code |
A1 |
Hirano; Toshiki ; et
al. |
March 30, 2006 |
Disk drive with support structure for disk-vibration capacitive
sensors
Abstract
A data recording disk drive has one or more capacitive sensors
for sensing out-of-plane vibration of the disk or disks. The
sensors are attached to a support structure that is attached to the
disk drive housing. Each sensor is associated with a disk and faces
a surface of the disk near the outer perimeter of the disk and
close to the recording head. The support structure can be made of a
metal or a high-strength plastic and can be a separate structure
mounted to the housing, or integrated as part of the single-piece
housing casting. If it is metallic, as would be the case if it were
integrated with the housing, then layers of insulating material
separate the sensors from the support structure. A support
structure that serves other functions in the disk drive can also
function as the support structure for the capacitive sensors.
Inventors: |
Hirano; Toshiki; (San Jose,
CA) ; Semba; Tetsuo; (San Jose, CA) ; White;
Matthew T.; (Mountain View, CA) |
Correspondence
Address: |
THOMAS R. BERTHOLD
18938 CONGRESS JUNCTION COURT
SARATOGA
CA
95070
US
|
Family ID: |
35539614 |
Appl. No.: |
10/956919 |
Filed: |
September 30, 2004 |
Current U.S.
Class: |
360/97.19 ;
G9B/33.024; G9B/5.198; G9B/5.202; G9B/5.216 |
Current CPC
Class: |
G11B 33/08 20130101;
G11B 5/58 20130101; G11B 5/5582 20130101; G11B 5/596 20130101 |
Class at
Publication: |
360/097.02 |
International
Class: |
G11B 33/14 20060101
G11B033/14 |
Claims
1. A data recording disk drive comprising: a housing; a spindle
motor attached to the housing and having an axis of rotation; at
least one disk mounted on and rotatable by the spindle motor about
said axis of rotation; at least one capacitive sensor comprising an
electrically conductive plate having a planar surface facing a
surface of said at least one disk; and a support structure attached
to the housing, said at least one sensor being mounted to the
support structure.
2. The disk drive of claim 1 wherein the housing comprises a base
and side walls, the spindle motor being attached to the base, and
wherein the support structure is mounted on the base.
3. The disk drive of claim 1 wherein the housing comprises a base
and side walls, the spindle motor being attached to the base, and
wherein the support structure is attached to a side wall.
4. The disk drive of claim 1 wherein the housing and support
structure comprise an integrated single-piece casting.
5. The disk drive of claim 1 wherein the support structure is
formed of electrically insulating material.
6. The disk drive of claim 1 wherein the support structure is
formed of electrically conductive material and further comprising
an insulating spacer located between said at least one sensor and
the support structure.
7. A data recording disk drive comprising: a housing; a spindle
motor attached to the housing and having an axis of rotation; a
plurality of axially-spaced disks mounted on and rotatable by the
spindle motor about said axis of rotation; a plurality of
capacitive sensors, each sensor comprising an electrically
conductive plate having a planar surface facing a surface of an
associated disk; and a support structure attached to the housing,
each sensor being mounted to the support structure.
8. The disk drive of claim 7 wherein the disk drive further
comprises a plurality of damping plates extending between the
axially-spaced disks, the damping plates extending
circumferentially around a sector of the disks and radially across
a radially outer annular region of the disks; and wherein each
damping plate is attached to said support structure.
9. The disk drive of claim 7 wherein each sensor is attached to an
associated damping plate.
10. The disk drive of claim 7 wherein the support structure
comprises a shroud located around a portion of the outer perimeter
of the axially-spaced disks for containing the air flow; and
wherein each sensor extends from the shroud to face its associated
disk surface near the outer perimeter of its associated disk.
11. The disk drive of claim 7 wherein the disk drive further
comprises a plurality of recording heads, a rotary actuator having
a plurality of arms that support the heads and extend between the
axially-spaced disks, and a plurality of air dams extending between
the axially-spaced disks for diverting air flow induced by the
rotating disks; and wherein each air dam is attached to said
support structure.
12. The disk drive of claim 11 wherein each sensor is attached to
an associated air dam.
13. The disk drive of claim 7 wherein the disk drive further
comprises a plurality of recording heads, a rotary actuator having
a plurality of arms that support the heads and extend between the
axially-spaced disks, and a plurality of ramps extending between
the axially-spaced disks for locating the heads away from the disks
when the disk drive is not operating; and wherein each ramp is
attached to said support structure.
14. The disk drive of claim 13 wherein the support structure and
ramps are a single-piece structure of plastic material, the
single-piece structure including spacer regions, each sensor being
attached to a spacer region.
15. A capacitive sensor assembly comprising: a support structure
having a plurality of generally parallel fingers; a plurality of
capacitive sensors, each sensor attached to a respective finger and
comprising a metallic plate having a planar surface.
16. The assembly of claim 15 wherein the support structure is
formed of electrically insulating material.
17. The assembly of claim 15 wherein the support structure is
formed of electrically conducting material and further comprising a
layer of insulating material located between each sensor and its
respective finger.
18. The assembly of claim 15 further comprising a capacitance
sensing circuit electrically connected to each sensor.
19. The assembly of claim 18 further comprising a multiplexer for
selecting one of the sensors for input to said sensing circuit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to data recording disk
drives, such as magnetic recording hard disk drives, and more
specifically to such disk drives that experience out-of-plane disk
vibration induced by air flow during rotation of the disks.
[0003] 2. Background of the Invention
[0004] Data recording disk drives have a stack of recording disks
rotated by a spindle motor, and an actuator that moves the
read/write heads across the surfaces of the rotating disks. Each
read/write head is formed on an air-bearing slider attached to one
end of a suspension. The suspension is attached at its other end to
a rigid arm of the actuator and allows the slider to pitch and roll
on a bearing of air generated by the rotating disk. The disk drive
actuator is typically a rotary voice coil motor (VCM) that moves
the actuator arm and the attached suspension and slider generally
radially to position the head at the desired track under the
control of a servo feedback control system that receives
pre-recorded servo position information from the disk. The trend in
future disk drives is a continual decrease in the spacing of the
concentric data tracks on the disk to increase the data storage
density, and a continual increase in the rotational speed of the
disk stack to decrease the data transfer time. As storage densities
and rotational speeds increase, the ability to position the
read/write heads to the proper data tracks and maintain the heads
on the data tracks becomes more difficult. As the disk-stack
rotational speed increases, air-flow turbulence near the perimeter
of the disks increases, which causes axial (out-of-plane) buffeting
or vibration of the disks (sometimes misleadingly called disk
"flutter"). These vibrations cause track-misregistration (TMR) of
the read/write heads and thus errors in reading data from and
writing data to the data tracks.
[0005] Concurrently filed application Ser. No. 60/______ filed
______, 2004 and titled "DISK DRIVE WITH CAPACITIVE SENSING OF DISK
VIBRATION AND FEEDFORWARD CONTROL FOR REMOVAL OF READ/WRITE HEAD
TRACK MISREGISTRATION" (Attorney Docket No. HSJ920040199US1)
addresses the problem of TMR caused by out-of-plane disk vibration
by use of capacitive sensors that sense the axial displacement of
the disks. The capacitive sensor associated with the disk surface
being accessed for reading or writing of data provides a signal to
a feedforward controller that provides a correction to the servo
feedback control system to thereby significantly reduce the effect
on TMR caused by out-of-plane vibration of the disk. The capacitive
sensors are located between the axially-spaced disks near the
perimeter of the disk stack and securely mounted to the disk drive
housing so that they do not experience vibration.
[0006] What is needed is a support structure for the capacitive
sensors that can be integrated with a conventional disk drive in a
low-cost manner without significant redesign of the disk drive
housing.
SUMMARY OF THE INVENTION
[0007] The invention is a disk drive with one or more capacitive
sensors for sensing out-of-plane vibration of the disk or disks.
The sensors are attached to a support structure that is attached to
the disk drive housing. Each sensor is associated with a disk and
faces a surface of the disk near the outer perimeter of the disk
and close to the path of the slider that supports the read/write
head.
[0008] The support structure can be a separate structure mounted to
the base or wall of the disk drive housing, or integrated as part
of the single-piece housing casting. The support structure can be
made of a metal or a high-strength plastic. If it is metallic, as
would be the case if it were integrated with the housing, then
layers of insulating material separate the sensors from the support
structure.
[0009] A support structure that serves other functions in the disk
drive can also function as the support structure for the capacitive
sensors. If the disk drive includes damping plates that extend
between the disks near their outer perimeter to reduce out-of-plane
disk vibration, the sensors can be supported by the damping plate
support structure or each sensor can be located on a corresponding
damping plate. If the disk drive includes a shroud surrounding the
disk stack for containing air flow inside the rotating disk stack,
the capacitive sensors can be supported by the shroud support
structure or integrated with the shroud. If the disk drive includes
air dams between the disks for diverting airflow away from the
head-suspension-arm assemblies, the capacitive sensors can be
supported by the air dam support structure or each sensor can be
located on a corresponding air dam. If the disk drive is a
"load/unload" type of disk drive that uses load/unload ramps that
extend between the disks, the sensors can be supported by the ramp
support structure.
[0010] For a fuller understanding of the nature and advantages of
the present invention, reference should be made to the following
detailed description taken together with the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a block diagram of a magnetic recording disk drive
incorporating the present invention.
[0012] FIG. 2A is a side view showing the spindle motor with the
disk stack and the support structure for the capacitive sensors
mounted to the disk drive housing.
[0013] FIG. 2B is a side view showing the support structure for the
capacitive sensors integrated into the single-piece housing
casting.
[0014] FIG. 3 is a schematic of a capacitance sensing circuit
coupled to the capacitive sensors.
[0015] FIG. 4A is a top view and FIG. 4B is a partial side
sectional view, respectively, of a disk drive with damping plates
and a plurality of capacitive sensors.
[0016] FIG. 5A is a top view and FIG. 5B is a partial side
sectional view, respectively, of a disk drive with a shroud located
near the outer perimeter for the disk stack and a plurality of
capacitive sensors.
[0017] FIG. 6A is a top view and FIG. 6B is a partial side
sectional view, respectively, of a disk drive with air dams located
between the disks and a plurality of capacitive sensors.
[0018] FIG. 7A is a top view of a disk drive with load/unload ramps
located between the disks and a plurality of capacitive
sensors.
[0019] FIG. 7B is a perspective view of the ramp support structure
in the disk drive shown in FIG. 7A.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 1 is a block diagram of a magnetic recording disk drive
incorporating the present invention. The disk drive includes a
housing 100 that supports a spindle motor 102 and a
voice-coil-motor (VCM) actuator 104. The housing 100 is typically a
single-piece metal casting with a base 180 and side walls, such as
side wall 182. A stack of magnetic recording disks, with the top
disk 110 being visible, is mounted on and rotatable by the spindle
motor 102. A read/write head 109 is associated with the top surface
of disk 110. The head 109 may be an inductive read/write head or a
combination of an inductive write head with a magnetoresistive read
head and is located on the trailing end of a slider 108. Slider 108
is supported on the actuator arm 106 by a suspension 107 that
enables the slider to "pitch" and "roll" on an air-bearing
generated by the rotating disk 110. The head, slider, suspension
and actuator arm are collectively referred to as a head-arm
assembly, and there is a stack of head-arm assemblies connected to
actuator 104, with each head-arm assembly being associated with a
corresponding disk surface.
[0021] The disk stack has a center of rotation about axis 111 and
is rotated in direction 115. Each disk surface includes a magnetic
recording layer with radially-spaced concentric data tracks. The
head must be maintained substantially on the centerline of a data
track to correctly read and write data. However, during operation
of the disk drive the head experiences track misregistration (TMR)
caused by various disturbances, including out-of-plane disk
vibration. Thus, each data track has a plurality of
circumferentially or angularly-spaced servo sectors that contain
head positioning information detectable by the head and used in a
servo feedback control system to maintain the head on the
centerline of the desired data track. The servo sectors in each
track are aligned circumferentially with the servo sectors in the
other tracks so that they extend across the tracks in a generally
radial direction, as shown by two typical servo sectors 117, 119.
The servo information read by the head is input as a
position-error-signal (PES) to a servo feedback controller 150 that
provides a control signal to VCM driver 155 to move the VCM
actuator 104 so that the head remains on the track centerline.
[0022] The disk drive according to the present invention
incorporates a plurality of capacitive sensors and a support
structure to address the problem of disk-vibration-induced TMR. A
capacitive sensor is associated with and faces each disk surface,
as shown by capacitive sensor 210 facing the top surface of disk
110. The capacitive sensors are attached to the disk drive housing
100 by a support structure 300. Each of the sensors is a plate
formed of metal or other electrically conductive material and is
located near the slider but outside the outer extent of the
generally radial path of the slider, as shown by sensor 210 and
slider 108 on the top surface of disk 110. Each sensor is located
close to its associated slider, i.e., the angle formed between the
line from the rotation axis 111 to the head 109 and the line from
the rotation axis 111 to the center of the sensor 210 should be
kept to a minimum. The capacitive sensor 210 has a surface area
large enough to provide a capacitive signal but small enough so
that it is detecting substantially only "local" axial displacement
of the disk, i.e., displacement near the slider 108. For a disk
drive with 95 mm diameter disks, the metallic plate forming the
sensor has a surface area of approximately 1 cm.sup.2. The spacing
between each sensor and its associated disk surface is in the range
of about 0.1 mm to 0.4 mm, which is a spacing selected to be close
enough for adequate sensor sensitivity yet far enough to avoid
contact between the sensor and the disk during an external shock to
the disk drive. The plates forming the capacitive sensors can be
made of aluminum, stainless steel, or other metal or metal alloy,
or other electrically conductive material, such as a conductive
plastic like carbon-filled PEEK (PolyEther-Ether-Ketone) or a
conductive ceramic like AlTiC (Aluminum-Titanium-Carbide).
[0023] The output of each capacitive sensor, such as sensor 210, is
converted by capacitance sensing circuit 250 to a voltage signal
that is sent to a feedforward controller 260. Feedforward
controller 260 provides a correction signal that is combined with
the output of feedback controller 150 to reduce the effect on TMR
caused by out-of-plane vibration of the disk.
[0024] Referring now to FIG. 2A, the capacitive sensors are
attached to a support structure 300 attached to the disk drive
housing 100. The housing 100 includes a base 180 and four side
walls, one of which is shown as side wall 182. Typically the
housing 100 is formed as a single-piece metal casting that includes
base 180 and the side walls. The spindle motor 102 is mounted to
the base 180 of housing 100 and supports the axially-spaced disks
110, 120, 130 making up the disk stack. Capacitive sensors 210,
220, 230 are associated with respective disks 110, 120, 130. The
sensors are attached to a support structure 300. The support
structure 300 is shown as being mounted to the base 180 of housing
100, but it can also be mounted to side wall 182. The support
structure 300 can be formed of an electrically insulating material,
such as a high strength injection-molded plastic, as shown in FIG.
2A, so that each metallic plate is electrically isolated from the
support structure and the other metallic plates.
[0025] The support structure 300 can also be formed of a metallic
material. Referring to FIG. 2B, the support structure is integrated
into the single-piece housing casting, in which case it is formed
of the same material as the housing, typically aluminum. If the
support structure is formed of a metallic material, either as a
separate structure mounted to the housing or as part of the housing
casting, then electrically insulating material is located between
each sensor and the support structure. As shown in FIG. 2B a
support structure 300' includes fingers 310, 320, 330 extending
between the disks 110, 120, 130 near the perimeter of the disk
stack and is integrated with side wall 182 as part of the
single-piece housing casting. Each sensor 210, 220, 230 is located
on and attached to a respective insulating layer 311, 321, 331 on
fingers 310, 320, 330, respectively. The insulating layers can be
formed of a plastic material, such as polyimide, that is bonded to
the fingers.
[0026] During vibration of the disk the distance between the sensor
and the disk surface, such as between sensor 210 and the top
surface of disk 110, will change and be detected as a change in
capacitance. The capacitance is inversely proportional to the gap
or distance between the sensor and the disk surface by the
relationship C=(.epsilon.A)/g, where .epsilon. is the permittivity,
A is the area of the sensor plate and g is the gap. FIG. 3 is an
exemplary schematic of a capacitance sensing circuit 250. The
outputs of the capacitive sensors, including sensor 210, are input
to a multiplexer. The disk drive controller (not shown), which has
selected the head that is reading or writing, provides a signal to
the multiplexer so that the capacitive sensor associated with the
disk on which the selected head is reading or writing is selected
as the input to the sensing circuit 250. The circuit is operated at
10 MHz and the signal from the selected sensor is input to a
capacitance bridge. Signals outside the range of interest are
removed by a high pass filter (HPF) and a low pass filter (LPF),
and the signal is amplified and output as a voltage. The voltage
signal out of circuit 250 represents the gap or distance between
the selected sensor and its associated disk surface and is sent to
the feedforward controller 260 (FIG. 1).
[0027] The disk drive described above has been illustrated as
having multiple disks in a stack and a plurality of capacitive
sensors on the support structure, with one sensor being associated
with each disk. However, the invention is applicable for a
single-disk disk drive with a single capacitive sensor on the
support structure. The disk drive may also have more than one
capacitive sensor per disk, e.g., there may be two sensors for each
disk with each sensor facing a respective one of the two disk
surfaces.
[0028] The support structure 300 described above is illustrated as
a separate structure dedicated to supporting the capacitive sensors
in the desired location relative to the disk stack. However, to
reduce fabrication cost the capacitive sensors can also be
supported by a support structure that serves other functions in the
disk drive. For example, if the disk drive includes damping plates
that extend between the disks near their outer perimeter to reduce
out-of-plane disk vibration, the sensors can be supported by the
damping plate support structure, or each sensor can be located on a
corresponding damping plate. If the disk drive includes a shroud
surrounding the disk stack for containing air flow inside the
rotating disk stack, the capacitive sensors can be supported by the
shroud support structure or integrated with the shroud. If the disk
drive includes air dams between the disks for diverting airflow
away from the head-suspension-arm assemblies, the capacitive
sensors can be supported by the air dam support structure, with
each sensor located on a corresponding air dam. If the disk drive
is a "load/unload" type of disk drive that uses load/unload ramps
that extend between the disks, so that when power to the disk drive
is removed each head-suspension assembly is moved up onto a ramp,
the capacitive sensors can be supported by the ramp support
structure.
[0029] FIG. 4A is a top view and FIG. 4B is a partial side
sectional view, respectively, of a disk drive with damping plates
extending over a radially outer annular sector of the region swept
by the rotating disks. The damping plates are supported on support
structure 400 which is integrally formed with the housing wall 182
as part of the fabrication of housing 100. However, the damping
plates may also be formed as a separate assembly and mounted to
base 180 or wall 182 after fabrication of housing 100. The support
structure supports damping plates 410, 420, 430, 440 that damp the
out-of-plane vibration of disks 110, 120, 130. Near the
circumferential end of the damping plates, in the region near the
sliders, as shown by section line A-A in FIG. 4A, the capacitive
sensors are attached to recesses in the damping plates. The
capacitive sensors 210, 220, 230 are secured to layers of
insulating material 411, 421, 431, respectively, located on
respective damping plates 410, 420, 430. Alternatively, the sensors
may be attached separately to and extend out from the support
structure 400, instead of being mounted on the damping plates.
[0030] FIG. 5A is a top view and FIG. 5B is a partial side
sectional view, respectively, of a disk drive with a shroud located
near the outer perimeter for the disk stack for containing the air
flow inside the stack of disks. The shroud has slits (not shown in
FIG. 5B) to permit movement of the actuator arms. The shroud is
supported by support structure 500 and has a cylindrical wall 502.
The support structure 500 can be formed of a plastic material and
mounted to housing base 180 with insulating spacer regions 510,
520, 530 between the capacitive sensors 210, 220, 230.
Alternatively, the support structure 500 can include the shroud
with radially inwardly directed fingers and be incorporated as part
of the metal single-piece housing casting, in which case each
capacitive sensor would be located on an associated finger with an
insulating layer between each sensor and the metal finger
supporting it.
[0031] FIG. 6A is a top view and FIG. 6B is a partial side
sectional view, respectively, of a disk drive with air dams located
between the disks for disrupting the air flow near the
head-suspension assemblies. A disk drive with air dams is described
in published patent application U.S. 2002/0036862 A1. A plastic
support structure 600 is mounted to the housing base 100 and
supports the radially inwardly extending air dams 610, 620, 630,
640. The capacitive sensors 210, 220, 230 are mounted on the air
dams 610, 620, 630, respectively. Alternatively, the support
structure 600 and the air dams can be incorporated as part of the
metal single-piece housing casting, in which case each capacitive
sensors would be located on an associated air dam with an
insulating layer between each sensor and the metal air dam
supporting it.
[0032] FIG. 7A is a top view of a disk drive with load/unload ramps
located between the disks for supporting the head-suspension
assemblies when the disk drive is not operating. FIG. 7B is a
perspective view of the ramp support structure 700. The ramp
support structure 700 is formed of plastic and mounted to the
housing base 100 and supports the ramps 710, 720, 730. The support
structure 700 has plastic spacer regions 711, 721, 731 that support
the capacitive sensors 210, 220, 230, respectively, and
electrically isolate the sensors from one another.
[0033] While the present invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made without departing from the spirit and scope
of the invention. Accordingly, the disclosed invention is to be
considered merely as illustrative and limited in scope only as
specified in the appended claims.
* * * * *